Insulator



Patented Sept. 11, 1928.

UNITED STATES testate PATENT DOUGLAS F. MINER, OF EAST PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC @a MANUFACTURING COMPANY, A CORPORATION OF EENNSYL- VAN IA.

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Application led September 23, 1924.

My invention relates to insulators and particularly to high-potential suspension 1nsulators of the cap-and-pin type.

`One object of my invention is to provide an insulator -of the above-indicated character, that shall be mechanically strong and that shall also distribute the electrostatic field between its terminals withsubstantially maximum efficiency consistent with mechanical considerations of an insulator of its particular type.

Another object of my invention is to provide a high-voltage suspension insulator unit for service in a series chain of similar units, in which all of the metal and insulating parts shall be formed in consideration not only of the parts of the unit itself but also in consideration of the parts of adjacent units to eectively distribute the electrostatic field. i

In Patent No. 1,129,520, issued Feb. 23, 1915, to K.. C. Randall, S. WL Farnsworth and C. L. Fortescue, is set forth an insulator, extending between two terminals of differ- K ent potential, having its surfaces conforming to the direction of the electrostatic field to provide substantially thesame dielectric strength asair along said surfaces. Patent No. 1,374,998, issued April 19, 1921, to C. L. Fortescue and G. I. Gilchrest shows a further development of this construction, together with the utilization of equipotential surfaces and the feature of having electrostatic and mechanical stresses coincide.

Since the teachings of the above-mentioned Randall et al patent, there has been a tendency in high-tension insulator and b-ushing development to adhere very closely to the flow-line and equipotential surface construction, it being` recognized that any considerable departure from this construction produces insulators of relatively low efciency. However, in certain branches of the insulator art, and particularly that branch relating to suspension insulators of the capand-'pin type, the above-mentioned features have not been extensively employed because of limitations imposed by mechanical considerations.

In other words, by reason of the peculiar mechanical construction, in which the pins are enclosed by the caps, and the longitudinal tension forces are resolved into diagonal component stresses through the insulator heads, and lother features necessary tothe Serial No. 739,257.

successful fulfillment of this mechanical duty, cap-and-pin insulators have retained certain features which have not adhered suficiently close to the features above discussed to render the insulators of maximum efficiency.

It is my aim to overcome the electrical deficiencies of cap-and-pin insulator, so far as the distribution of the electrostatic field between the caps and pins is concerned, and to retain certain of the mechanical features which are necessary to provide proper strength.

Accordingly, I provide a cap-and-pin insulator in which the cap is provided with a perimetral flange having both mechanical and electrical functions, a pin formed to co- Y operate both mechanically and electrically with said flange and an insulating member especially formed to so cooperate with both the cap and the pin as to provide a suspension insulator of the cap-and-pin type that is provided more nearly with flow-line and equipotential surfaces than has, to the best of my knowledge, heretofore been suggested.

Figure 1 of the accompanying drawings is a side view, partially in elevation and partially in section, of an insulator of practical form constructed in accordance with my invention, and

Fig. 2 is a diagrammatic view of conducting elements for illustrating the plan from which the structure of Fig. 1 is derived.

As in a usual insulator of the cap-and-pin type, my invention comprises, in general, an insulating member having a head portion 1 of inverted substantially cup-shape and a petticoat portion 2, a metal-cap terminal member 3 and a metal-pin terminal member 4.

However, in contradistinction to the usual cap-and-pin insulator, the insulator head portion 1 is provided with a portion 6 havsurface of the insulating member, to provide roughened areas bywhich bodies of cement 16 and 17 adhere more effectively to the insulator. V'These bands are preferably slightly offset with respect to each other along the longitudinal axis of the insulator to resolve longitudinal mechanical load forces into diagonal components between the inner portions 11 and 12 of the pin 4 and the iiange 8 of the cap 3. These features have, so far as the mechanical functions thereof are concerned, been suggested before but the cap and pin have not been formed to the particular shapes shown because, in this insulator, they also function to distribute the electrostatic field therebetween in a particular manner, to be described.

In priorinsulators, the inner end 11 of the pin 4 and the flange 8 of the cap 3 have been formed for mechanical considerations only and, while they have, in general, had adjacent sloping surfaces somewhat similar to those of my insulator, they have also had relatively sharp edges which concentrate electrostatic stresses and, thereby lower the dielectric strength of the insulator.

Considering the device shown in Fig. 2, the cap 3 and the pin 4 are here shown without regard to the mechanical consideration of the insulator of Fig. 1. With any metal cap and any metal pin thereon, as shown, and a difference of potential between them, there is an electrostatic field therebetween, as indicated by the dotted lines.

If the caps 3 were of uniform thickness having cylindrical shape and a flat closed end or bottom, there would be a very severe concentration of the field at the edge 8 regardless of the shape of the pin 4. Also, the field between the sides of the cap and the inner end of the pin would be of different strength from the field between the pin and the position of joinder between the sides and the bottom of the cap. These conditions are remedied by -making the closed end or bottom of the cap 3 spherical, the edge 8 thereof enlarged and of gradually curved contour merging into the sides of the cap, and the pin 4 cylindrical on its sides and spherical on its inner end. By this construction, as shown in Fig. 2, the internal field between the cap and the pin is rendered almost uniform in strength and distribution throughout, and the stresses are relatively widely distributed adjacent to the edge 8 of the cap 3.

However, with the above construction and the outer end of the pin 4 and having sharp edges, as in the former insulators, there would still be concentration of the eld at the outer end of the pin. Hence, the enlarge vment or spherical portions 10 widely distributes the field and with the above mentioned features renders the field of maximum distribution or of minimum concentration.

Were the cap 3 of the next lower unit, as indicated at the bottom of Fig. 2, of different construction having sharp edges or pro-Il for maximum electrical efficiency and the shapes of the parts have been sufficiently retained in the device of Fig. 1 to insure substantial maximum electrical efficiency and, at the same time, to include the mechanical features above described.

In other words, the spherical vinner end 11 of the pin 4, together with the slightly concave shank portion 12 thereof, cooperate with the inturned flange 8 to provide substantially maximum mechanical strength, and

these parts are so shaped as to insure substantially maximum electrical strength.

The enlarged outer end 10 of the pin 4l constitutes a hollow socket in which a projection or ball terminal 18 .on the cap 3, for connection to the socket, is shielded from the electrostatic field.

The surface 7 conforms to the outer surface of the enlarged end 10 of the pin 4 and all of the other surfaces of the insulat ing member, including the inner and outer surfaces of the head portion 1 and the upper and lower surfaces of the petticoat 2 are either similarly at right angles to the field at substantially every point thereon or lie substantially parallel to the field, as does the under' surface of the insulator portion 6.

By my invention, a cap-and-pin insulator having all of the mechanical advantages of one of the most effective of its type is prov1de d that is rendered more electrically effective and less likely to injury from electrical causes.

While I have shown and described a particular form of my invention, changes may be made therein without departing from the spirit and scope thereof,as set forth in the appended claims.

I claim as my invention:

1. An insulator of the cap-and-pin type, comprising a metal cap having closed-end surfaces of gradual curvature and an openend perimeter of torus-shape having a relatively great radius, the surfaces of said torus merging gradually into the side surfaces of the cap, a metal pin having a shank portion opposite said closed-end and side cap surfaces shaped to uniformly distribute cement between the the electrostatic field between the shank and said surfacesy and an enlarged substantially spherical outer end to widely distribute the field between the sphere and the torus, and an insulating member having a hollow head portion in said cap and oversaid shank and a petticoat portion projecting laterally outwardly between said sphere and said torus, the surfaces of said insulating member being shaped as substantially equi-potential and How-line surfaces in the electrostatic field as determined by the surfaces of the cap and pin.

2. insulator of the comprising a metal cap having closed-end surfaces of gradual curvature and an openend perimeter of torus-shape having a relatively great radius, the surfaces of said torus merging gradually into the side surfaces of the cap, and the torus constituting an annular shoulder inside said open-end perimeter, a metal pin having a shank portion opposite said closed-end and side cap surfaces shaped to uniformly distribute the electrostatic field between the shank and said surfaces and an enlarged substantially spherical outer end to widely distribute the field between the sphere and the torus, said shank having an enlarged inner end, an insulating member having a hollow head portion in said cap and over said shank and a etticoat portion projecting laterally outwardly between said cap-and-pin type,

' sphere and said torus, the surfaces of said insulating member being shaped as substantially equi-potential and flow-line surfaces in the electrostatic field as determined by the surfaces of the cap and pin, a body of shank and the insulator head, and a body of cement between the insulator head and the cap, the enlarged head of the pin and said annular shoulder being related to each other and to said bodies of cement to transmit tension forces diagonally through said hollow head.'

3. An insulator of the cap-and-pin type comprising a metal cap having closed-en surfaces of gradual curvature and an openend perimeter of torus-shape having a relatively great radius, the surfaces of said torus merging gradually into the side ,surfaces of the cap, said cap also having a headed projection at the center of its outer end surface constituting a connector portion, a metal pin having a lshank portion opposite said closed-end and side cap surfaces shaped to uniformly distribute the electrostatic field between the shank and said surfaces and an enlarged substantially spherical outer end to widely distribute the field between the sphere and the torus, said sphere being hollow and constituting a receiving socket connector for a headed projection similar to theheaded projection on the cap, and an insulating member having a hollow head portion in said cap andover said shank and a petticoat portion projecting laterally outwardly between said sphere and said torus, the surfaces of said insulating member being shaped as substantially equipotential and flow-line surfaces in the electrostatic eld as determined by the surfaces of the cap and pin, and said sphere enclosing said second headed projection similar to the projection on the cap to prevent disturbance of the field thereby,

4. An insulator comprising a cap having conducting side surfaces, conducting closedend surfaces of gradual curvature and an open-end perimeter of substantially torus shape having a relatively surfaces of said torus being conducting and merging gradually into said side surfaces, a pin element having a conducting-surface shank portion opposite said closed-end and side surfaces shaped to uniformly distribute the electrostatic lield between the shank and said cap surfaces, a connector element for cooperation with the outer end of the pin, one of said elements having an enlarged substantially spherical conducting-surface portion to widely distribute the field between the sphere and the torus, and an insulating member having a hollow head portion in said cap and over said shank and a petticoat portion projecting laterally outwardly between said sphere and said torus, the surfaces of said insulating member being shaped as substantially equi-potential and -flow-line surfaces in the electrostatic field as deter mined by the surfaces of the cap and pin,

In testimony whereof l have hereunto subscribed my name this 18th day of September, l92l DUGLAS MNER.

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